Diol compounds are widely used as a starting material for preparing polyesters or polyurethanes. Among these, alicyclic diols such as 1,4-cyclohexanedimethanol (CHDM) have been used for the purpose of improving the performance of the polymer, for example, heat resistance, water resistance, weatherability, or transparency.
The polyester compound generally used as a molding material has an aromatic ring introduced into its structure. For example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and the like are used. These polyester compounds are widely used as fibers, films, sheets or other molding materials because of their good mechanical and chemical properties. However, such typical polyester compounds comprising an aromatic dicarboxylic acid component and an aliphatic diol component also have crystalline properties. Therefore, despite their good heat resistance, the transparency of these polyester compounds is insufficient for use as films or sheets. PET has a relatively high ester group concentration and further is disadvantageous in that it has poor resistance to hydrolysis.
The above-described problems may be solved by replacing the entire or a part of the terephthalic acid component of the polyester having high crystallinity such as PET and PBT, with a dicarboxylic acid such as isophthalic acid or adipic acid, or by replacing the entire or a part of the diol component with another diol, for example, an aliphatic diol such as 1,4-cyclohexanedimethanol, 1,6-hexanediol, or a polyetherdiol such as polyethylene glycol, to thereby reduce the crystallinity. However, when these components are used, the polyester usually has a fairly low glass transition temperature Tg as compared with, for example, PET having a Tg of 69.degree. C.
In other words, when these components are copolymerized, the crystallinity is reduced but the heat resistance is also greatly reduced and therefore, the molded article thus obtained has poor high temperature performance. In order to overcome this problem, the use of some alicyclic diols has been proposed. For example, JP-A-50-27892 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-A-50-28595 propose a polyester using 1,1-cyclohexanedimethanol as the diol starting material, however, the heat resistance and transparency are insufficient.
Diol compounds also have been used for manufacturing polyurethanes in two ways. One is a method of directly reacting a diol with the isocyanate group (a diol used as a so-called "chain elongating agent"), and the other is a method of using a polyesterpolyol as the polyol component of the polyurethane.
It is known that a polyurethane obtained by reacting 4,4-methylenebis (phenylisocyanate) (MDI) which is one of the most commonly used diisocyanates, with a diol, for example, ethylene glycol, has a Tg of 139.degree. C. and a polyurethane obtained by reaction with 1,4-butanediol has a Tg of 109.degree. C. (see, Polymer Handbook, 4th ed.). Polyurethanes using a diol having a long chain, a polyetherpolyol or a polyesterpolyol are liable to have a low Tg. When these polyurethanes are used as plastics, the main chain thereof is deficient for applications requiring heat resistance, and a cross-linking component such as a trifunctional or greater functional polyisocyanate compound must be introduced at the molding step.
The present applicant has proposed a polyurethane (JP-A-2-274715) using a specific alicyclic polyol compound as a polyurethane having a high heat resistance as compared with the above-described polyurethanes.
The polyesterpolyol as a starting material of a polyurethane has conventionally been produced by condensing a glycol such as ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol or neopentyl glycol, or a polyol such as trimethylolpropane, glycerin or pentaerythritol, with a polycarboxylic acid such as adipic acid, maleic acid or phthalic acid.
The polyurethane obtained by polyaddition reacting the thus-produced polyesterpolyol with a polyisocyanate is used as a urethane foam, elastomer, RIM molded article, coating material, coating agent, fiber raw material or adhesive.
The polyurethane derived from the above-described polyesterpolyol has relatively good mechanical properties and heat resistance, however, it is deficient in that its hydrolysis resistance is inferior as compared with a polyether glycol or a polycarbonate diol and therefore, its application range is limited.
A diol having relatively large aliphatic groups has been proposed for increasing the hydrolysis resistance of polyurethane. A polyesterpolyol comprising an ethylene glycol or a diol such as 1,4-butanediol or 1,6-hexanediol as the diol component has crystalline properties and has a melting point higher than room temperature. Therefore, some difficulties may arise in reacting with a polyisocyanate.
As a result of extensive investigations, the present inventors have found that the above-described problems of the prior art can be solved by using a diol compound having a specific alicyclic skeleton as the diol component of a polyester or a polyurethane. The present invention has been accomplished based on this finding.